This application claims the priority benefit of Japanese Patent Application No. 11-207537, filed Jul. 22, 1999, the entire subject matter of which is incorporated herein of reference.
1. Field of the invention
The invention relates to a method for correcting characteristics of an attenuated phase-shift mask. Specifically, the characteristics of the attenuated phase-shift mask is modified by changing a thickness or a composition of a mask pattern layer in response to a particular data.
2. Description of the related art
With an increase in the level of integration of semiconductor integrated circuits, there have been rapid advances in minimizing micropatterns used for circuitry, so that a high resolution technology and a sufficient depth of focus (DOF) has been required. Therefore, a conventional photomask 1 shown in FIG. 14, which includes a light shielding layer 16 formed on a glass substrate 2 to form micropatterns, cannot satisfy the requirements of the resolution and the DOF in a high integration lithography process because the light passing through the mask 1 is diffracted.
To resolve this problem, a variety of types of phase-shift mask has been proposed to date, including an attenuated phase-shift mask, a Lebenson-type phase-shift mask, a phase-shift mask having an optical proximity correction, a self-align phase-shift mask and a transmittance-type phase-shift mask. Specifically, the attenuated phase-shift mask is widely used because of its simple construction.
The attenuated phase-shift mask 10 shown in FIG. 2 includes a attenuated layer 14 which is formed on a glass substrate 12, and a light shielding layer 16 form on parts of the attenuated layer 14. Referring to FIG. 15, when light passes through the mask 10, a phase xcex81 of the light that passes through the attenuated layer 14 is shifted from a phase xcex82 of the light that passes only through the substrate 12 for about 180 degree because the transmitting speed of the light that passed through the attenuated layer 14 becomes slow. As a result, the light which passes through around the border between the attenuated layer 14 and the substrate 12 is setoff by the phase difference. Therefore, the resolution can be improved.
However, it is difficult to control a thickness and a quality of the attenuated layer. As the attenuated layer is formed on the substrate by a vacuum evaporation method, the thickness and the quality of the attenuated layer are easily influenced by the changes of the process environments or conditions. Therefore, a required transmittance and phase difference of the mask cannot be obtained. Further, once the attenuated phase-shift mask having an unsatisfied attenuated layer is formed, a required transmittance and phase difference of the mask cannot be modified by additional evaporation processes.
An objective of the invention is to resolve the above-described problem and to provide a method for correcting characteristics such as a transmittance and a phase difference, of an attenuated phase-shift mask.
The objective is achieved by a method for correcting characteristics of an attenuated phase-shift mask having an attenuated layer including (a) storing a data in a memory, which shows a correlation between characteristics and process conditions, (b) measuring the characteristics of the attenuated phase-shift mask, (c) calculating a appropriate process condition from the result of the step (b) and the data stored in the memory; and (d) soaking the attenuated phase-shift mask into a liquid solution for a certain time that is calculated in the step (c) to change thickness and composition of the attenuated layer.